1. Field of Invention
The present disclosure relates to a technology of driving an LED string. More particularly, the present disclosure relates to a voltage regulation circuit for regulating a voltage loaded on a current regulator in an LED driving apparatus.
2. Description of Related Art
In the prior art, when an LED string is connected to a DC voltage source for operation, in general, a current regulator is required to be connected in series with the LED string, so as to stabilize the working current of the LED string by using the constant current characteristic of the current regulator. For example, a voltage conversion module can be used to convert a DC or AC input voltage to a constant DC voltage, and the DC voltage is electrically connected to the current regulator, so as to provide a working voltage for LED string.
In various actual application situations of the LED string, a plurality of LED driving modules are often adopted and connected in parallel to the DC voltage (i.e. the output voltage of the voltage conversion module). Each LED driving module includes a current regulator and an LED string connected in series with the current regulator. Due to the property differences among different LEDs, even two LED strings with the same number of LEDs may have different working voltages. Therefore, to keep the LEDs of each LED string working normally, the output voltage of the voltage conversion module should be set to a voltage value slightly higher than a maximum working voltage of the LED string. That is, the output voltage has to provide a safety margin relative to the maximum working voltage.
Furthermore, the current regulator and the LED string of each LED driving module are connected in series. The current regulator needs to hold a differential voltage between the output voltage VO and the working voltage VF of the LED string. The higher differential voltage results in a larger loss of the current regulator, and the energy consumption of the system is increased accordingly. For example, if the output voltage of the voltage conversion module is constantly a 24V DC voltage; the LED string has 6 LEDs; and the voltage drop of each LED is 3V when working normally, then the voltage drop of the current regulator connected in series with the LED string is 6V, and the current flowing through the current regulator is equal to the current of the LED string. Therefore, the loss of the current regulator is large and the system efficiency is low.
In view of the foregoing, those skilled in the industry are endeavoring to find ways to design a voltage regulation circuit for enabling the output voltage of the voltage conversion module to be self-regulated according to the current flowing through the LED string and meanwhile reducing the loss of the current regulator and promoting the system efficiency without affecting the brightness of the LED string.